Despite rampant rumors on the development of a turbocharged V6, Mercedes-Benz has chosen to continue with a naturally aspirated V8 engine in the next generation of the SLK AMG that is due to make its first public outing at the Frankfurt Motor Show this fall.

While we only get to see a fuzzy photo of the 2012 SLK 55 AMG, the firm with the three-point star emblem revealed plenty of details around the roadster model’s new eight-cylinder engine.

The naturally aspirated M152 engine is based on the AMG M157 5.5-litre V8 biturbo unit found in E 63 AMG, CLS 63 AMG, S 63 AMG and CL 63 AMG. Compared to the previous V8, output has increased by 62HP to 422-horses while peak torque is up from 510 to 540Nm (U.S. spec model: 415HP at 6,800 rpm and 398 lb-ft at 4,500 rpm).

The aluminum V8 engine features the AMG Cylinder Management system that can shut off four-cylinders from 800 to 3,600 rpm to improve fuel efficiency. Mercedes says that the switch from four to eight-cylinder operation is “immediate and imperceptible” taking a mere 30 milliseconds at 3,600 rpm.

According to the Germans, the new SLK 55 AMG returns a combined fuel consumption of 8.5 lt/100 km, a staggering 3.5lt or 30% less than that of the preceding model with the less potent 360HP V8.

We expect Mercedes to drop the full details on the 2012 SLK 55 AMG just before the Frankfurt Motor Show.

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